1. Field of the Invention
The present invention relates to a communication apparatus and a computer program product.
2. Background Art
Conventionally, as a technique of automatic identification, RFID (Radio Frequency Identification) is known. Specifically, RFID is a technique in which an RFID reader/writer communicates by near field communication using an electromagnetic field or radio wave to read information or write information stored in an RFID tag.
As an RFID tag, a passive type (passive tag) is usually used. The passive tag does not include a cell, and when an electromagnetic wave or radio wave is received from the RFID reader/writer, an electric current occurs and is rectified to be used as electric power to drive the RFID tag itself. Most RFID tags are formed from a configuration in which the electric power of reception is used as the driving power for responding to the RFID reader/writer.
According to such configuration, the RFID tag cannot generate driving electric power to operate the RFID tag unless the RFID tag is near the antenna of the RFID reader/writer to a certain extent, and the communication distance is usually at a close range. Although the situation differs depending on frequency band and shape of antenna, the maximum communication distance of a battery driven portable terminal such as a PDA (Personal Digital Assistant), a handy terminal, etc. is about 20 mm.
Moreover, there is known a wireless communication apparatus in which transmission output level is reduced to prevent interruption of communication by a strong magnetic field from an antenna when a noncontact IC card (RFID tag) as a communication target comes near (For example, see Japanese Unexamined Patent Application Publication No. 2006-54703).
RFID is used for the purpose of not only reading information from an RFID tag attached to equipment for counting inventory in a warehouse or an RFID tag attached to merchandise for managing inventory in a store, etc., but also for the purpose of using the RFID tag as an authentication key of a portable terminal including an RF reader/writer function.
In a configuration in which polling is performed for the purpose of such authentication, the RFID reader/writer section of the portable terminal constantly continues to perform monitoring operation of whether or not there is an RFID tag within the communication range (detection operation of RFID tag) while waiting to login.
Polling is processing which periodically performs inquiry of a search for an RFID tag (whether there is a request for transmission). When there is a response that there is a transmission request from an RFID tag, the communication starts.
Therefore, polling is performed by periodically and continuously emitting an electromagnetic field from the RF reader/writer section during the detection operation of the RFID tag. Consequently, the operation time of the portable terminal becomes short due to the electric power consumption by output of the electromagnetic field.
With the above conventional wireless communication apparatus which reduces transmission output level, the consumed electric power can be reduced when the transmission output level is reduced. However, the communication range (communication distance) also becomes small.
Moreover, in a configuration in which polling is performed, it is possible to consider a configuration in which the interval of polling is large in order to reduce consumption of electric power. However, the detection operation of the RFID tag becomes slow which worsens usability of the portable terminal.